The invention relates to a method and an apparatus for conditioning gas before and after the high pressure is relieved.
Many combustible gases are either naturally at high pressure, or are brought to it through technology. Natural gas pumped from underground deposits, for instance, is at a high pressure, as are gases in underground gas reservoirs or large pressure vessels. Gases that are relieved from high pressure to a lower pressure, for instance during pumping, removal from reservoir storage, or in a gas turbine, cool down severely as a consequence of the expansion. This presents several technical problems, because inflow lines for instance can ice up, or the physical properties of the gases change, or the readiness to ignite is diminished. To overcome these technical disadvantages and to compensate for the cooling down, the gas is heated before or after the pressure relief. Typically, however, this heating is done before the pressure relief, or in other words while the gas is at high pressure.
As conventional, typical preheater units, especially for underground natural gas reservoir systems, two different systems are primarily employed: Gas preheating systems, and gas heaters. Typically, both types of system include three components: heat generation, heat exchangers, and the heat carrier system. They differ only in their embodiment or in their three-dimensional arrangement. In the gas preheating system, the gas which is at reservoir pressure is passed through a heat exchanger. There the reservoir gas is heated, and the corresponding carrier medium, such as a mixture of water and glycol, is cooled down in countercurrent in parallel pipelines. The heat carrier medium is then reheated in a closed loop and returned to the heat exchanger. Regulating the gas temperature is usually accomplished via the flow rate of the heat carrier through the heat exchanger; the quantity of heat carrier medium depends on the reduction in the gas temperature after the pressure relief. However, it is also possible to control the gas temperature by regulating the flow rate of the reservoir gas. Beyond the heat generation, heat exchanger and heat carrier system components, the expense in terms of equipment for the preheating system extends to a boiler housing for the heat exchanger and to the safety and control system for both the boiler unit and the heat carrier system. The delivery of heat can be done by combusting liquid or gaseous fuels, through electrical energy, or by using gas heating pumps.
Gas heaters are preheating devices in which both heat generation and the heat transfer to the reservoir gas flowing through are done in a single step. The heaters are horizontal containers that are equipped with flame pipes in their lower portion and pipe banks in their upper portion; the interstices are filled with heat carrier medium. The reservoir gas and the natural gas needed for heating the water bath pass through the gas heater in opposite directions, and the heat carrier medium is heated by the flame pipes. The regulation of the gas temperature is done here directly at the heat exchanger, by adjusting the fuel flow to suit the amount of heat required. In contrast to preheating systems, natural gas heaters are set up entirely out in the open, and the expense for equipment extends not only to the components already named above but beyond that to safety and control devices for both the fuel gas and the reservoir gas.
In a departure from the basic concepts presented above, it has been proposed in International Patent Disclosure WO 94/11626 of Kxc3xcck et al. that the gas be heated in a heat exchanger, as in the above two systems, before the expansion. Here, though, the heating is to be done with the aid of the exhaust gas from small block heating and power station, and an internal gas combustion engine and a generator are used. The exhaust gas from the combustion engine heats up the reservoir gas in a heat exchanger before the expansion. Through the block heating and power station, driving the generator generates electrical energy, which can be fed into the power grid.
European Patent EP 0 453 007 to Verweij is an original variant of the above systems. It too uses an internal combustion engine, usually a gas engine, and along with exhaust gases the waste heat from the engine and the air needed for combustion are also utilized to heat the gas. The gas is cooled down in a countercurrent in a heat exchanger before being used in the engine. Correspondingly more heat exchangers are used, and it is proposed that one heat exchanger be used upstream and the other downstream of the expansion of the reservoir gas. Once again, the combustion engine drives a generator, which generates electrical energy.
U.S. Pat. No. 4,871,308 to Norton et al. pertains to a system for heating a flow of liquid. In it, separate gas flows of natural gas and air are fed in a controlled, compressed manner into an injection and mixing zone, with one gas being expanded and the other being compressed, and are then carried into a combustion system, and the exhaust gases are used via a heat exchanger to heat a liquid. This system can also be used to heat reservoir gases.
It is a common feature of all the methods described above that they heat the gas flow of the reservoir gas only indirectly, through heat exchangers or carrier mediums. In principle, the gas is first heated before the pressure relief occurs, or in other words while still at high pressure in the heat exchanger. The proposed apparatuses with combustion systems disadvantageously require official permits and demand a large amount of safety technology. The energy is obtained either from the combustible gas or from a gas boiler fired with natural gas. The most pronounced disadvantage of the systems described, however, is an ecological deficit, since none of the systems described can utilize 100% of the combustion heat of the calorific value consumed in the prior art. The efficiency of the systems used until now is correspondingly low; that is, the energy consumption necessary to achieve the desired effect is correspondingly high.
There has accordingly been a need for an apparatus or a method which dispenses with a combustion system for which an official permit must be obtained, and which for environmental reasons achieves high utilization of the combustion heat of the energy consumed. The system should also meed the needs for an ecologically appropriate and economical energy supply.
According to the invention, it is now proposed that an apparatus in accordance with the main claim be used.
It has surprisingly been demonstrated, in a series of texts, that it is possible for the gas flow of a combustible gas that is at high pressure to be combusted in a controlled way in a closed container, and thus for the gas to be heated continuously.
Combustible gas escapes from a reservoir at high pressure. It flows through a pipeline up to a point where oxygen is added, in either pure or dilute form. This addition can be done via a gas distributor, which communicates with an ignition device and a flame monitor, or via a burner. There, controlled combustion takes place, and the quantity of oxygen or oxygen-containing gas that has to be added is controlled via a temperature measurement. When the gas is heated by direct combustion in the pipeline, water is produced, among other components; this water may be in liquid form and is caught in a trap before the pressure relief of the gas. The heated gas, saturated with water vapor, is then relieved to a different, lower pressure in some suitable apparatus or device, such as a throttle valve or a gas turbine. This is followed by the temperature sensor and usually a further trap, to whichxe2x80x94as is usual in the prior artxe2x80x94a drying system, for instance in the form of a glycol scrubber, is connected.
In the present invention, it has proved advantageous in some cases to perform the combustion with pure oxygen or an arbitrary mixture of oxygen and air, instead of with pure air. To avoid overly high temperatures, the combustion can also be promoted by the use of a suitable catalyst.